The rifles originally came out in 1870, chambered for the 10.35mm or .41 cartridge, which was basically a centrefire version of the Swiss Vetterli cartridge. These were all single-shot bolt rifles, and were surprisingly advanced for their period.
In 1887 the Vitali box magazine was adapted to this rifle and adopted for it. Early rifles were converted to take the magazine, and subsequent production was built with the magazines already in place. This gave the shooter 4 rounds in the box magazine.
In 1915, many of these early rifles were converted to take the 6.5x52 Carcano cartridge which Italy had adopted as the Model 1891. The conversion consisted of a tube soldered into the barrel to sleeve it for the newer round, alterations to the bolt face and extractor, and the installation of a new magazine assembly so that the rifle could take a Mannlisher-type clip; pieces of wood were let into the forestocks at this time to take up space where the Vitali magazine (which was very wide because of its central coil spring) had been removed.
For ammunition, regular 6.5 Carcano is safe but marginal for the conversions. Nice thing is that you can handload the stuff and keep pressures even lower than they already are. These rifles can be very accurate, but, boy!, are they ever heavy to lug around!
For an original rifle, you can make up ammo using .348 Winchester brass. RCBS has dies for this number. Try a cast bullet with no more than 20 grains of SR4759 as a start load and see what that does.
These are one of the lesser-known rifles of the black-powder period, which is really too bad, as they were very advanced in their design.
And they are a LOTTA fun to shoot!
Got my first one more than 40 years ago and still have it, a 6.5 conversion; some day, I'm gonna be rich enough to get a .41.